From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH] mm: vmpressure: don't count userspace-induced reclaim as
 memory pressure
Date: Thu, 23 Jun 2022 18:37:02 +0200
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To: Yosry Ahmed <yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>, Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>, David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Miaohe Lin <linmiaohe-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, NeilBrown <neilb-l3A5Bk7waGM@public.gmane.org>, Alistair Popple <apopple-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>, Suren Baghdasaryan <surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Peter Xu <peterx-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux-MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>

On Thu 23-06-22 09:22:35, Yosry Ahmed wrote:
> On Thu, Jun 23, 2022 at 2:43 AM Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> wrote:
> >
> > On Thu 23-06-22 01:35:59, Yosry Ahmed wrote:
[...]
> > > In our internal version of memory.reclaim that we recently upstreamed,
> > > we do not account vmpressure during proactive reclaim (similar to how
> > > psi is handled upstream). We want to make sure this behavior also
> > > exists in the upstream version so that consolidating them does not
> > > break our users who rely on vmpressure and will start seeing increased
> > > pressure due to proactive reclaim.
> >
> > These are good reasons to have this patch in your tree. But why is this
> > patch benefitial for the upstream kernel? It clearly adds some code and
> > some special casing which will add a maintenance overhead.
> 
> It is not just Google, any existing vmpressure users will start seeing
> false pressure notifications with memory.reclaim. The main goal of the
> patch is to make sure memory.reclaim does not break pre-existing users
> of vmpressure, and doing it in a way that is consistent with psi makes
> sense.

memory.reclaim is v2 only feature which doesn't have vmpressure
interface. So I do not see how pre-existing users of the upstream kernel
can see any breakage.

-- 
Michal Hocko
SUSE Labs